1. Field of the Invention
The present invention relates in general to optical disk storage systems and more particularly, to a method and apparatus for providing high speed optical disk recording.
2. Description of the Related Art
In recent years, optical disk devices have been used to record or reproduce large amounts of data. Optical disks are storage mediums from which data is read and to which data is written by laser. Each optical disk can store a large amount of data, typically in the order of 600-700 Mbytes. Such optical disk devices are under active technical developments for achieving higher recording density.
There are generally two methods of controlling the rotating speed of an optical speed. The first is constant linear velocity (CLV) recording, in which constant linear velocity is provided during recording by varying the speed of the spindle motor when recording proceeds from the inner to the outer diameter of the disk. The second is constant angular velocity (CAV) recording, in which constant angular velocity is provided during recording, while changing the frequency of data recording when recording proceeds from the inner to the outer diameter of the disk.
Current writable optical disks include spiral-shaped grooves in the dye coated layer (on the disk) that is sensitive to laser beams. The groove is not a perfect spiral, but wobbled in order to obtain motor control and timing information. Recording is implemented in the groove by locally heating up the sensitive layer with a laser spot. The laser output is modulated with the information to be recorded. The parts of the disc that were heated up during recording show a reflection decrease after recording and are called pits. The encoded Audio or Data information is stored in the length of these pits and in the distances between them. These lengths and distances only take discrete values.
The data synchronization and address information for the disk is provided through a signal typically referred to as a wobble signal. The wobble signal is typically a frequency modulated signal with bi-phase coded address information called Absolute Time in Pre-Groove (ATIP).
In CLV recording, the motor speed at the inner diameter is typically high, and gradually decreases as the optical head moves toward the outer diameter. In CAV recording, the spindle motor operates at a constant speed, but the data recording frequency varies as the optical head moves from the inner diameter to the outer diameter of the disk. The recording speed in optical disk recording is typically limited due to two factors. The first arises due to mechanical limitations in providing maximum rotational speed at the inner diameter. The second arises due to limitations in electronic data recording rate at the outer diameter.
To increase the speed of writing on optical disks, some drives utilize a Zoned CLV recording in which the disc is divided into a few zones. In a given zone, the CLV speed, or the data rate is constant while rotational speed decreases. At the beginning of each zone, the rotational speed is the same and thus the method utilizes the maximum mechanical speed limitation. However, as the CLV recording speed, or the data rate increases, it becomes increasingly difficult for the servo loop to keep the recorded data in synchronism with the ATIP due to electromechanical limitations. In addition, the Zoned CLV recording requires stopping the recording at the zone boundary and going back to re-link the recorded segment of the previous zone. Similarly, as the CAV recording speed increases, it also becomes increasingly difficult for the electronic circuits to keep up the data rate and may reach the data rate limitation. In this situation, a seamless writing transition from CAV method to CLV method becomes very desirable. This is called a Partial CAV recording method.
Currently, in partial CAV recording, a technique known as pseudo CLV motor speed control is typically utilized. In this technique, the motor speed control is provided while in CAV mode. The motor speed reference is gradually changed in steps according to a prescribed way to emulate CLV. In using such a technique, the ATIP address needs to be constantly monitored and the reference speed must be constantly changed, requiring additional servo overhead.
Accordingly, there is a need in the technology to overcome the aforementioned problems. There is also a need in the technology to obtain maximum recording speed efficiency without interruption during writing on a disc.